Question

我花了好几天（好，晚上）来解决这个问题。在线上有如此多的示例适用于不同版本的Android Studio，不同版本的Android，不同版本的OpenCV，但我无法将其中任何一个带入最终的“正常工作”阶段。

这个示例（基于youtube tutorial，我到了需要许可的地步。很好，我在其中添加了内容并进行了检查，然后弹出询问用户相机权限。但是，屏幕保持黑屏。我已经进行了logcat调试，似乎所有正确的方法都被调用了。希望对您有所帮助。

代码：

Manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mytestopencvapp" >

    <uses-permission android:name="android.permission.CAMERA"/>


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme" >
        <activity android:name=".MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

MainActivity.java

package com.example.mytestopencvapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceView;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.JavaCamera2View;
import org.opencv.android.JavaCameraView;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;

public class MainActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener2 {

    private static String TAG = "MainActivity";

    JavaCameraView javaCameraView;
    Mat mRGBA, mRGBAT;

    private final int PERMISSIONS_READ_CAMERA=1;

    BaseLoaderCallback baseLoaderCallback = new BaseLoaderCallback(MainActivity.this) {
        @Override
        public void onManagerConnected(int status) {
            Log.d(TAG, "callbacksuccess");
            switch (status)
            {
                case BaseLoaderCallback.SUCCESS:
                {
                    Log.d(TAG, "case success");
                    javaCameraView.enableView();
                    break;
                }
                default:
                {
                    Log.d(TAG, "case default");
                    super.onManagerConnected(status);
                    break;
                }

            }

        }
    };

    static
    {
        if (OpenCVLoader.initDebug())
        {
            Log.d(TAG, "OpenCV is intialised");
        }
        else
        {
            Log.d(TAG, "OpenCV is not initialised");
        }
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate");
        setContentView(R.layout.activity_main);
        javaCameraView = (JavaCameraView)findViewById(R.id.my_camera_view);
        javaCameraView.setVisibility(SurfaceView.VISIBLE);
        javaCameraView.setCvCameraViewListener(MainActivity.this);

// Here, thisActivity is the current activity
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {

            // Permission is not granted
            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    Manifest.permission.CAMERA)) {
                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.
            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.CAMERA},
                PERMISSIONS_READ_CAMERA);

                // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
                // app-defined int constant. The callback method gets the
                // result of the request.
            }
        } else {
            Log.d(TAG, "PERMISSIOns granted");
            // Permission has already been granted
        }


    }

    @Override
    public void onCameraViewStarted(int width, int height) {
        Log.d(TAG, "onCameraViewStarted");
        mRGBA = new Mat(height, width, CvType.CV_8UC4);
    }

    @Override
    public void onCameraViewStopped() {
        Log.d(TAG, "onCameraViewStopped");
        mRGBA.release();
    }

    @Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame)
    {
        Log.d(TAG, "onCameraFrame");
/*        mRGBA = inputFrame.rgba();
        mRGBAT = mRGBA.t();
        Core.flip(mRGBA.t(), mRGBAT, 1);
        Imgproc.resize(mRGBAT, mRGBAT, mRGBA.size());
        return mRGBAT;*/

        mRGBA = inputFrame.rgba();
        Core.transpose(mRGBA, mRGBAT);
        Imgproc.resize(mRGBAT, mRGBAT, mRGBAT.size(),0,0,0);
        Core.flip(mRGBA.t(), mRGBA, 1);
        return mRGBA;
    }


    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy");
        if (javaCameraView != null)
        {
            javaCameraView.disableView();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause");
        if (javaCameraView != null)
        {
            javaCameraView.disableView();
        }

    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume");
        if (OpenCVLoader.initDebug())
        {
            Log.d(TAG, "OpenCV is intialised again");
            baseLoaderCallback.onManagerConnected((BaseLoaderCallback.SUCCESS));
        }
        else
        {
            Log.d(TAG, "OpenCV is not working");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, baseLoaderCallback);
        }
    }
}

我的res布局activity_main.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <org.opencv.android.JavaCameraView
        android:id="@+id/my_camera_view"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        />


</RelativeLayout>

据我所知，我已经正确链接了它们，可以确认OpenCV的初始化，检查并授予了权限，但是然后... JavaCameraView只是黑色的。

Answer 1

您需要告诉CameraView相机权限已被授予。您可以通过调用setCameraPermissionGranted()函数来实现。该函数调用应进入您的onCreate方法中的“ permit allowed”块中，如下所示：

if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
        != PackageManager.PERMISSION_GRANTED) {
    // More code here ...
} else {
    Log.d(TAG, "Permissions granted");
    javaCameraView.setCameraPermissionGranted();
}

此外，对于尚未授予许可的情况，您可能想在onRequestPermissionsResult()中调用此函数。 onRequestPermissionsResult()函数位于您的Activity类中。当授予或拒绝该权限的用户请求应用程序发出时，将调用此方法。可能如下所示：

@Override
public void onRequestPermissionsResult(
        int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {

    // Ensure that this result is for the camera permission request
    if (requestCode == PERMISSIONS_READ_CAMERA) {
        // Check if the request was granted or denied
        if (grantResults.length > 0
                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            // The request was granted -> tell the camera view
            javaCameraView.setCameraPermissionGranted();
        } else {
            // The request was denied -> tell the user and exit the application
            Toast.makeText(this, "Camera permission required.",
                    Toast.LENGTH_LONG).show();
            this.finish();
        }
    } else {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }
}

有关Android权限系统的更多信息，请查看以下资源：

Request App Permissions该站点介绍了使用所有必要步骤来请求权限的过程。
Permissions Overview该站点在清单文件中包含有关uses-feature的信息。您可能需要在清单文件中添加以下行：<uses-feature android:name="android.hardware.camera" android:required="true" />，以防止在没有摄像头的设备上安装。

现在您将看到onCameraFrame回调函数实际上已被调用。由于NullPointerException未初始化，因此将导致mRGBAT。要仅查看相机图像，您可以直接在此函数中返回inputFrame.rgba()。这将至少显示摄像机图像。所有其他步骤都是正常的图像处理，以旋转/镜像图像。

Answer 2

我在android 10中也遇到了同样的问题，经过大量的反复试验，我发现必须在main Activity中实现以下方法：

@Override
protected List<? extends CameraBridgeViewBase> getCameraViewList() {
        return Collections.singletonList(mOpenCvCameraView);
    }

Android OpenCV相机示例仅显示黑屏

2 个答案: